In the prior art, a vehicle or equipment may be configured with a controller area network (CAN) data bus or another network data bus that supports communication between controllers and other network elements. The vehicle data bus communicates signals over a transmission line, such as one or more twisted pairs of wire or a coaxial cable, for example. If the transmission line is cut or damaged, communications over the network data bus can be impaired, intermittent or absent. Physical visual inspection of the transmission line may not be practical or possible where the cable is routed through conduit, sheathing, frame members, unibody vehicle structures, body panels, or other equipment structures. Thus, there is a need for an alternative method and system for diagnosing a fault or open circuit in a network.